Essentially, the work concerned a six-protein subcomplex, the Vo-ATPase section of the V-ATPase. In most eukaryotes, this is composed of six proteins of two types (5+1), but in yeast it's composed of six proteins of three types (4+1+1). The paper describes how bioinformatics was used to deduce the likely last common ancestor of two of the yeast proteins, they then synthesised genes encoding the proteins to express them in yeast cells and conducted experiments to see how they functioned.

To cut a long story short, they make some interesting discoveries about how gene duplication followed by sequence divergence can lead to increasingly complex structures, even where the sequence changes are neutral or individually disadvantageous. It's also indicative of how the 'molecular machines' that ID creationists love to portray as impossible to explain using evolutionary theory actually may have arisen...by evolutionary mechanisms.